gistfile1.rb

class Sample2 < ActiveRecord::Base
  validate :check_start_date_and_end_date

  def check_start_date_and_end_date
    if start_date.nil?
      errors.add(:start_date, "start date should not be nil")
    end
    if end_date.nil?
      errors.add(:end_date, "end date should not be nil")
    end

    return unless errors.empty?

    if start_date > end_date
      errors.add(:start_date, "start date should be past of end date")
      errors.add(:end_date, "start date should be past of end date")
    end

    if end_date - start_date <  1.hour
      errors.add(:start_date, "start date and end date should have one hour gap")
      errors.add(:end_date, "start date and end date should have one hour gap")
    end
  end
end